Lettering sets, including a pigmented plastic display layer backed by an adhesive layer, to be computer cut and retained in position on a transparent stripable release sheet, are familiarly used for applying athletes' names, numbers and team logos to their athletic garments. Three-layer lettering sets, using a pigmented polyvinyl chloride plastic lettering display sheet backed by a sheet of adhesive and having a transparent front release sheet, which aids in positioning on garments or other substrates, are described in U.S. Pat. Nos. 5,112,423 and 5,441,785 to Liebe. Outlines of lettering elements in mirror-image are cut starting through the adhesive sheet and through the lettering sheet, to and sometimes into but not through, the release sheet.
In another form, lettering sets are made with a pigmented polyvinyl chloride (PVC) display layer with an adhesive backing sheet but without the paper forward sheet on which the PVC was originally cast. The cutting proceeds in direct, not mirror-image, order, first through the pigmented layer and then through the adhesive layer. After the portion between the lettering outlines have been removed, a handling sheet, usually a transparent sheet whose surface is somewhat adherent, is pressed against the forward side of the lettering elements to lift them and position them in place on a garment or other substrate.
Polyvinyl chloride materials are inexpensive but require temperatures of about 320.degree. .F to form a film. PVC materials may contain solvents to aid in spreading and casting the display layer film. U.S. Pat. No. 5,312,645 suggests that a solvent-based polyurethane may be substituted for PVC to gain improved tensile strength, abrasion resistance and capacity for elongation. A film of a solvent-based polyurethane may be formed at a temperature necessary for solvent evaporation, which may be as low as ambient temperature.
A problem associated with solvent-based materials being used as pigmented display layers is that the choice of the material of the release or casting sheet is limited to materials that are resistant to the solvents used in the pigmented display layer and resistant to the temperature of the solvent evaporation process. Typically, paper and polyester release or casting sheets are used in the manufacture of lettering sets because of their resistance to solvent and heat distortion.
It would desirable to be able to use a release sheet that is more flexible than the typical paper or polyester release sheets. It also would be desirable to be provide a release sheet that is thin to achieve greater flexibility.